1. Field of the Invention
This invention relates generally to an apparatus for recording and reproducing a digital signal and particularly to an apparatus for recording and reproducing a digital signal made in the form of successive data blocks, and a block address circulating with a predetermined phase relation to a certain reference signal.
2. Description of the Prior Art
In the case of pulse code modulation (PCM) system tape recorder of fixed head type, it is known that, when a magnetic tape is transported at a predetermined speed, a servo pulse is recorded on the magnetic tape so as to have a predetermined frequency, and on playback, a phase-locked loop (PLL) servo circuit is employed to phase-compare the reproduced servo pulse with a reference phase signal to produce a compared output by which the running speed of the magnetic tape is controlled. But, when the phase of the servo pulse is varied considerably before and after an edit operation involving splice-edition and simple electronic edition, the phase compared output becomes a large one and the running speed of the magnetic tape is overly varied thereby so that sometimes the time base of the reproduced data varies considerably. Because of this the clock can not be extracted from the reproduced data and a time base error or variation beyond the correction range of a time base corrector (TBC) will take place. As an example of the TBC, the same assignee of this application, has previously proposed the U.S. application Ser. No. 06/298,522 which was filed on Sept. 1, 1981.
Furthermore, in the PCM-system tape recorder, a sync recording is carried out to record a digital signal so as not to lose continuity for the previously recorded digital signal. In this case, a preceding playback head or transducer is used to record a new signal so as to produce a relationship relative to the block address and the like, that is the same as the predetermined recording format. Therefore, the generation phase of the block address must be changed before and after the phase jump of the servo pulse occurs.